1. Field of the Invention
This invention relates generally to transmitting rotating power in a motor vehicle driveline. More particularly, it pertains to reversing the rotational direction of an input, between a transmission output, connected to the input, and the wheels of the vehicle.
2. Description of the Prior Art
The powertrain of a hybrid electric vehicle includes multiple power sources, an internal combustion engine (ICE), principally used when highway speeds are sustained; an electric motor for charging electric storage batteries, and a traction motor for launching the vehicle, i.e., for accelerating the vehicle from a stopped condition.
In an electric hybrid powertrain for a passenger car, reverse drive is usually produced by a small traction electric motor whose torque capacity is relatively low and is unamplified by the powersplit transmission in the powertrain. The traction motor alone is driven in reverse to launch an electric hybrid vehicle in a reverse direction without assistance from the ICE or torque amplification provided by a transmission or transaxle.
An electric hybrid vehicle that is equipped with all-wheel drive (AWD) or four-wheel drive (4WD) and is expected to tow a heavy load or to be operated on rough terrain may have inadequate reverse drive torque capacity because the output torque of the traction motor is too low for those operating conditions.
Adding reverse gearing to the transmission itself is difficult. There is a need in the industry to increase the magnitude of wheel torque provided in reverse drive especially in the powertrain of electric hybrid vehicle equipped with AWD or 4WD, which is expected to tow a heavy load or to be operated on rough terrain.